This invention relates to the transmission and reception of signals via satellite and, more particularly, to the use of an antenna system for illuminating a specifically shaped region of earth terrain by either multiple beams or by a shaped beam from a common antenna borne by the satellite.
Satellite communication is often employed for transmission of a signal from one point on the earth's surface to be received at another point or over a specific region of the earth's surface. To accomplish this mission, it has been the practice to employ two antennas of two communication systems carried by a single satellite in synchronous orbit. The first system is a multi-beam TDMA (time division multiplex antenna) satellite communications system which is an effective way for increasing earth station power flux density by providing a high gain, narrow beam, spacecraft antenna. Increased signal power flux density allows increased transmission capacity and a smaller and more economical earth stations. On the other hand, the second system is a shaped beam FDMA (frequency division multiplex antenna) satellite communication system which is efficient for a large number of accesses to earth stations. Conventionally, to implement the two systems, two separate antennas are used, one antenna providing a multi-beam link and the second antenna providing the shaped beam link. Each antenna is a reflector antenna.
A problem arises in that the two reflector antennas needed for service take up a large part of the satellite and, therefore, may exclude the possibility of placing on the satellite additional antennas which might be required for further frequency bands of operation. Thus there is a need for reduction of the overall space required for accomplishing the two antenna functions.